Fluid pressure control device with a failure alarm for a vehicle brake system

ABSTRACT

A device for a brake system including two independent hydraulic lines extending from a dual type brake master cylinder and connected to the respective rear wheel brakes. The device is compactly formed with its essential parts housed in a single casing and can be readily mounted across the two hydraulic lines midway thereof to serve two functions, one of warning the driver of any fluid leakage possibly occurring in one or the other of the two hydraulic lines and the other of adjusting the ratio of the front to the rear wheel brake pressure for maximized overall braking efficiency. A pair of differential pistons are slidably fitted in aligned cylinder bores to define in each an input and an output hydraulic chamber communicating with each other through a normally open control valve, which is closed upon movement of the associated piston under differential pressure. Also, a balance piston is arranged between the differential pistons and movable with either of them to actuate a switch unit inserted in an electrical alarm circuit.

BACKGROUND OF THE INVENTION

This invention relates generally to brake systems for automotivevehicles of the type including a dual type brake master cylinderassociated with two mutually independent hydraulic lines and moreparticularly to fluid pressure control devices for such brake systemswhich include a brake failure alarm.

As is well known, in one form of brake system of the type described, thefirst and second hydraulic lines, extending from the respective outletports of the dual type brake master cylinder, are connected to the brakechambers in respective pairs of front and rear wheels lying on theopposite sides of the vehicle. In another form, the front wheel brakesare each provided with two hydraulic chambers respectively connectedwith the first and second hydraulic lines, which are connected to therespective rear wheel brakes.

SUMMARY OF THE INVENTION

The present invention has for its object the provision of a fluidpressure control device with a failure alarm which is usable in vehiclebrake systems of the type described and highly effective to ensuredriving safety.

A further object of the present invention is to provide a fluid pressurecontrol device of the character described which is compact inconstruction and easy to handle.

According to the present invention, a fluid pressure control device witha failure alarm is provided which includes means for automaticallywarning the driver of any fluid leakage possibly occurring in either ofthe two mutually independent hydraulic fluid lines L₁ and L₂ of thebrake system and means for automatically adjusting the ratio ofhydraulic pressure in the front wheel brakes to that in the rear wheelbrakes to a prescribed value thereby to give a maximized overall brakingefficiency, and in which both of said means are housed in a commoncasing of generally cylindrical form.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the general arrangement ofone preferred embodiment of the present invention;

FIG. 2 is a diagram similar to FIG. 1, illustrating the generalarrangement of another preferred embodiment of the invention;

FIG. 3 is a partly schematic cross-sectional plan view of the essentialparts of the device shown in FIGS. 1 and 2;

FIG. 4 is a graphic representation of the hydraulic pressurecharacteristics obtainable at the rear wheel brakes according to thepresent invention; and

FIG. 5 is a graphic representation of the hydraulic pressurecharacteristics obtainable at the front wheel brakes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, there is shown a vehicle brake system embodying the presentinvention and which includes a first and a second hydraulic fluid line,L₁ and L₂, respectively extending from the two output ports of a dualtype brake master cylinder M and connected to the respective pairs offront and rear wheel brakes, Bf', Br and Bf, Br', lying on the oppositesides of the vehicle. FIG. 2 illustrates another brake system embodyingthe present invention and in which each of the front wheel brakes Bf andBf' includes two hydraulic chambers respectively connected with thefirst and second brake lines L₁ and L₂. In each of these figures,reference numeral 3 indicates the casing body of the device of thepresent invention, which is arranged across the first and secondhydraulic lines L₁ and L₂ between the brake master cylinder M and therear wheel brakes Br and Br'.

Referring to FIG. 3, the dual type brake master cylinder M is of knowntandem structure, including an integral piston assembly comprised of apair of front and rear pistons 2₁ and 2₂, which are operable under theaction of a brake pedal 1 to feed the first and second hydraulic linesL₁ and L₂ with pressure fluid such as oil under pressure, respectively,through a first and a second outlet port P₁ and P₂ of the brake mastercylinder M.

The casing 3 of the device of the present invention has defined thereina pair of axially aligned left and right cylinder bores 4₁ and 4₂, whichare adapted to be closed at the outer end by threaded plugs 5₁ and 5₂,respectively. Reference numeral 3a indicates a partition wall formed inthe casing to separate the cylinder bores 4₁ and 4₂ from each other andin which wall a bearing aperture 6 of limited diameter is formed.Accommodated in the cylinder bores 4₁ and 4₂ are a pair of differentialpistons 7₁ and 7₂ of the same size and respective pressure adjustingsprings 8₁ and 8₂ arranged to bias the pistons 7₁ and 7₂ axiallyoutwardly. Also, a balance piston 9 is slidably fitted in the bearingaperture 6. The differential pistons 7₁ and 7₂ are formed therein withrespective small stepped cylinder bores 10₁ and 10₂ and minor pistons12₁ and 12₂ of the same diameter are slidably fitted in the largerdiameter portions of the respective cylinder bores 10₁ and 10₂ withrespective annular seals 11₁ and 11₂ arranged on the outside of thepistons 12₁ and 12₂. The balance piston 9 is formed on the opposite endsthereof with axially extending aligned stems 9₁ and 9₂, which areslidably fitted through the respective minor pistons 12₁ and 12₂ axiallythereof. Abutment rings 13₁ and 13₂ are secured to the extremities ofthe respective stems 9₁ and 9₂ for abutting engagement with the annular,interior shoulder surface of the respective differential pistons 7₁ and7₂. Seat plates 14₁ and 14₂ are arranged in the cylinder bores 4₁ and4₂, respectively, between the differential piston 7₁ or 7₂ and theadjacent pressure adjusting spring 8₁ or 8₂ for bearing engagement withthe back or inner end face of the respective minor pistons 12₁ and 12₂.

Further, the minor pistons 12₁ , 12₂ and stems 9₁, 9₂ of the balancepiston 9 define in the respective stepped cylinder bores 10₁ and 10₂ afirst and a second input hydraulic chamber a₁ and a₂, respectively.Further, the differential pistons 7₁ and 7₂ define in the cylinder bores4₁ and 4₂ a first and a second output hydraulic chamber b₁ and b₂,respectively, in co-operation with the threaded plugs 5₁ and 5₂. Asillustrated, the first and second input hydraulic chambers a₁ and a₂ arein communication with the upstream portions of the first and secondhydraulic lines L₁ and L₂, respectively, by way of inlet ports 15₁ and15₂ formed in the wall of casing 3. The first and second outputhydraulic chambers b₁ and b₂ are in communication with the downstreamportions of the hydraulic lines L₁ and L₂, respectively, by way ofoutlet ports 16₁ and 16₂ formed in the wall of casing 3.

The end walls of the respective stepped cylinder bores 10₁ and 10₂ areformed inside thereof with valve seats 17₁ and 17₂, respectively, andare also formed with axial oil apertures 18₁ and 18₂, respectively,opening into the adjacent output hydraulic chambers b₁ and b₂. Ballvalves 19₁ and 19₂ engageable with the respective valve seats 17₁ and17₂, and springs 20.sub. 1 and 20₂ for biasing the ball valves intoclosed position are accommodated in the respective stepped cylinderbores 10₁ and 10₂. Extending into the oil apertures 18₁ and 18₂ arevalve opening rods 21₁ and 21₂ which extend axially inwardly from theinner end faces of the respective threaded plugs 5₁ and 5₂. These valveopening rods 21₁ and 21₂ are so arranged as to hold open the respectiveball valves 19₁ and 19₂ at the end of axial outward movement of therespective differential pistons 7₁ and 7₂.

The balance piston 9 is formed with an annular groove 22 in its medialportion fitted in the bearing aperture 6 in the partition wall 3a and aswitch unit 23, including an actuator 24 normally engaged in the annulargroove 22, is threadably fitted in the wall of casing 3. The switch unit23 has normally open contacts which are closed when the switch actuator24 is forced out of the annular groove 22 as the balance piston 9 ismoved to the right or the left and, as shown, as electric circuit 28 isformed between the terminal 25 of the switch unit 24 and the casing 3,including an alarm device 26 in the form of a lamp, a buzzer or the likeand a voltage supply source 27.

Description will next be made of the operation of the device describedabove.

Normally, when the brake master cylinder M remains inoperative, the leftand right differential pistons 7₁ and 7₂ are in their outermost positionunder the initial bias of the respective pressure adjusting springs 8₁and 8₂, as shown in FIG. 3, and the ball valves 19₁ and 19₂ are heldopen for fluid communication between the first input and outputhydraulic chambers a₁ and b₁ and between the second input and outputhydraulic chambers a₂ and b₂, respectively, through the oil apertures18₁ and 18₂.

Under this situation, if the brake pedal 1 is actuated, the hydraulicoutput of the brake master cylinder M is fed into the entire lengths offirst and second hydraulic lines L₁ and L₂ to cause the front wheelbrakes Bf, Bf' and the rear wheel brakes Br, Br' to operate all at thesame time. With the rise of the output fluid pressure of the brakemaster cylinder M, the fluid pressure in the input and output hydraulicchambers a₁, a₂, b₁ and b₂ reaches a definite level such that thepressure differential acting upon the pistons 7₁ and 7₂, each havingopposite end faces differing in effective area from each other, causesthe respective pistons 7₁ and 7₂ to move axially inwardly against thebias of the pressure adjusting springs 8₁ and 8₂. As a result, the ballvalves 19₁ and 19₂ are seated against the respective valve seat 17₁ and17₂ to close the oil apertures 18₁ and 18₂ so that the hydraulicpressure in the rear wheel brakes Br and Br' is reduced by an amountcorresponding to the increase in volume of the first and second outlethydraulic chambers b₁ and b₂ as resulting from the axial movement of therespective differential pistons 7₁ and 7₂.

As the output pressure of brake master cylinder M further increases, thepressure increase in the respective input hydraulic chambers a₁ and a₂acts to push the differential pistons at this time axially outwardly andthe ball valves 19₁ and 19₂ are again opened to increase the pressure inthe output hydraulic chambers b₁ and b₂. When this pressure reaches adefinite level, it causes the differential pistons 7₁ and 7₂ again tooperate and is accordingly reduced. With repetition of the operationdescribed, the brake fluid pressure in each of the rear wheel brakes Brand Br' varies along the bent line in FIG. 4. The point of inflexion pis determined by the initial load set on the pressure adjusting springs8₁, 8₂ and the rate of pressure rise after the point of inflexion p isdetermined by the ratio of the area of one end face of the pressurereceiving pistons 7₁, 7₂ to that of the other end face thereof.

On the other hand, the front wheel brakes Bf and Bf' are directlysubjected to the output fluid pressure of the brake master cylinder M;that is to say, the fluid pressure in the front wheel brakes is heldequal to the output pressure of the brake master cylinder M, asillustrated in the diagram of FIG. 5.

Accordingly, with the device of the present invention, the front wheelbrakes Bf and Bf' can work forcefully upon the front wheels, which arerequired to bear an increasing downward load as the vehicle is tiltedforwardly under the effect of heavy braking operation, while the rearwheel brakes Br and Br' work relatively lightly upon the rear wheels,which are more or less relieved of the downward load with the forwardtilt of the vehicle. Thus, all the four wheels of the vehicle can bebraked as a whole with a maximized efficiency without the danger of anyskidding.

Further, in such normal braking operation described above, since thepressures in the first and second input hydraulic chambers a₁ and a₂ areheld equal to each other, the balance piston 9 remains in its neutralposition illustrated, with the switch actuator 24 remaining inengagement with the annular groove 22 in the medial portion of thepiston 9 and the contacts of the switch unit 23 held open to maintainthe alarm 26 inoperative.

However, if there exist some fluid leakage, for example, in the secondhydraulic line L₂, the pressure in the second input hydraulic chamber a₂cannot be effectively raised even when the brake master cylinder M isactuated and hence the balance piston 9 is subjected to an increasedfluid pressure only on the end face of the left-hand side stem 9₁ andthus moved to the right together with the right-hand side minor piston12₂ and adjacent annular seal 11₂ until the abutment ring 13₂ on theright-hand side stem 9₂ is brought into abutting engagement with theannular shoulder surface of the adjacent differential piston 7₂.Simultaneously with this, the switch actuator 24 is forced out of theannular groove 22 to close the electric circuit 28 and thus the alarm 26is actuated. The balance piston 9, once placed in its extreme rightposition, remains in that position due to the frictional drag exerted bythe annular seals 11₁ and 11₂ upon the respective stems 9₁ and 9₂ evenafter the brake master cylinder M has been released to exhaust the firstinput hydraulic chamber a₁ and accordingly the alarm 26 is keptoperative until the pressure failure or leakage in the second hydraulicline L₂ is remedied.

After the failure has been remedied, the pressure in both inputhydraulic chambers a₁ and a₂ is naturally raised as the brake mastercylinder M is actuated so that the right-hand side minor piston 12₂,previously moved to its extreme right position and now subject to theraised pressure in the second input and output hydraulic chambers a₂ andb₂, is moved to the left together with the annular seal 11₂ intoabutting engagement with the seal plate 14₂, embraced between thepressure adjusting spring 8₂ and differential pistion 7₂, and actsthrough the medium of the seat plate 14₂ to restore the balance piston 9to its neutral position. Simultaneously with this, the switch actuator24 is released into engagement with the annular groove 22 in the balancepiston 9, thereby indicating that now no pressure failure exists in thewhole hydraulic system.

In the event of a fluid leakage in the first hydraulic line L₁, thebalance piston 9 operates in quite the same manner as described aboveexcept that its direction of operation is reversed.

It will be apparent from the foregoing description that, according tothe present invention, the brake fluid pressure in the left and rightrear wheel brakes Br and Br', respectively connected with the first andsecond mutually independent hydraulic lines L₁, and L₂, is normallyreduced at a prescribed ratio with respect to that in the front wheelbrakes B_(f) and B_(f) ' so that all the four wheels of the vehicle aresubjected to respective braking forces corresponding to the load levelsimposed thereon upon a braking operation. Further, in cases where afluid leakage occurs in one or the other of the two hydraulic lines L₁and L₂, the driver is warned of such trouble without fail. In addition,since the component parts required to serve these functions are sodesigned as to be accommodated compactly in a single casing, such asindicated at 3, the device is highly convenient to handle and can beeasily mounted on a vehicle even where only a limited space isavailable.

While one preferred form of the device of the present invention has beenshown and described, it will be apparent to those skilled in the artthat many changes and modifications may be made therein withoutdeparting from the spirit of the invention or the scope of the appendedclaims.

What is claimed is:
 1. In a vehicle brake system of the type including adual brake master cylinder having a first and a second independentoutput port and a first and a second hydraulic fluid line extending fromsaid respective first and second output ports of said brake mastercylinder and connected to the respective hydraulic fluid chambers of apair of left and right front wheel brakes, a fluid pressure controldevice with a failure alarm comprising: a casing arranged across saidfirst and second hydraulic fluid lines midway thereof and defining apair of aligned left and right cylinder bores, a pair of left and rightdifferential pistons slidably fitted in said respective cylinder bores,a first and a second input hydraulic chamber defined on the axiallyinner side of said respective differential pistons and communicatingwith respective upstream portions of said first and second hydraulicfluid lines, a first and a second output hydraulic chamber defined onthe axially outer side of said respective differential pistons andcommunicating with respective downstream portions of said first andsecond hydraulic fluid lines, said differential pistons each having oneend face exposed to the adjacent input hydraulic chamber and the otherend face exposed to the adjacent output hydraulic chamber and larger inarea than said one end face, a fluid control valve provided for fluidcommunication between each of said input hydraulic chambers and theadjacent output hydraulic chamber, means secured to said casing foropening each said fluid control valve upon axial movement to theoutermost position of the associated differential piston and to closesaid valve upon axially inward movement thereof, a balance pistonslidably fitted at the opposite ends in said first and second inputhydraulic chambers and slidable from a neutral position under a pressuredifferential occurring between said input hydraulic chambers, and aswitch unit operable in response to the sliding movement of said balancepiston from the neutral position to actuate an external alarm.
 2. Avehicle brake system as claimed in claim 1 wherein each saiddifferential piston has a bore therein establishing communicationbetween the adjacent input and output chambers, said fluid control valvecomprising a valve member for selectively opening and closing said borein response to the axial movement of the differential piston.
 3. Avehicle brake system as claimed in claim 2 wherein said valve member isa ball valve.
 4. A vehicle brake system as claimed in claim 2 comprisingspring means acting on said valve member and the balancing piston tourge said valve member to close said bore.
 5. A vehicle brake system asclaimed in claim 2 wherein said means for opening each valve comprises astem fixed to the casing and extending through the associated bore of arespective differential piston to engage the respective valve member andurge the same to open said bore.
 6. In a vehicle brake system of thetype including a dual brake master cylinder having a first and a secondindependent output port and a first and a second hydraulic fluid lineextending from said respective first and second output ports of saidbrake master cylinder and connected to the respective hydraulic fluidchambers of a pair of left and right front wheel brakes, a fluidpressure control device with a failure alarm comprising: a casingarranged across said first and second hydraulic fluid lines midwaythereof and defining therein a pair of aligned left and right cylinderbores on opposite sides of a partition wall thereof, a pair of left andright differential pistons slidably fitted in said respective cylinderbores and each having a small cylinder bore formed therein on theaxially inner side thereof, a pair of left and right minor pistonsslidably accommodated in said respective small cylinder bores of saiddifferential pistons in fluid-tight relation therewith, a first and asecond input hydraulic chamber respectively defined by the interiorsurfaces of said differential piston bores and one end face of saidminor pistons and communicating with respective upstream portions ofsaid first and second hydraulic fluid lines, a first and a second outputhydraulic chamber defined on the axially outer side of said respectivedifferential pistons and communicating with respective downstreamportions of said first and second hydraulic fluid lines, spring meansacting to resiliently bias said respective differential pistons inaxially outward directions, means for defining innermost limit positionsof said minor pistons in their axial movements within said differentialpiston bores, said differential pistons each having one end face exposedto the adjacent input hydraulic chamber and the other end face exposedto the adjacent output hydraulic chamber and larger in area than saidone end face, a fluid control valve provided for fluid communicationbetween each of said input hydraulic chambers and the adjacent outputhydraulic chamber and adapted to open upon axial movement to theoutermost position of the associated differential piston and close uponaxially inward movement thereof, a balance piston slidably carried bysaid partition wall of said casing and having a pair of left and rightaxial stems formed on the opposite ends so as to extend therefromthrough said respective minor pistons to said first and second inputhydraulic chambers, said balance piston being held in a neutral positionunder the centering action of said minor pistons in the normal operatingcondition of said brake system and being slidable from the neutralposition under a pressure differential occurring between said inputhydraulic chambers, and a switch unit operable in response to thesliding movement of said balance piston from the neutral position toactuate an external alarm.
 7. A vehicle brake system as claimed in claim6 comprising means secured to said casing for opening each said fluidcontrol valve upon axial movement of the associated differential pistonto its outmost position and for closing said valve upon axially inwardmovement of said differential piston.
 8. A vehicle brake system asclaimed in claim 7 wherein each said differential piston has a boretherein establishing communication between the adjacent input and outputchambers, said fluid control valve comprising a valve member forselectively opening and closing said bore in response to the axialmovement of the differential piston.
 9. A vehicle brake system asclaimed in claim 8 wherein said valve member is a ball valve.
 10. Avehicle brake system as claimed in claim 8 comprising spring meansacting on said valve member and the associated stem of the balancepiston to urge said valve member to close said bore in the associateddifferential piston.
 11. A vehicle brake system as claimed in claim 8wherein said means for opening each valve comprises a stem fixed to thecasing and extending through the associated bore of a respectivedifferential piston to engage the respective valve member and urge thesame to open said bore.